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docs(bigquery): add sample to read from query destination table (#9964)
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This sample addresses internal issue 134774673, in which we recieved
feedback that it's not clear how to paginate through the results of a
query. This sample shows that all completed queries have a destination
table, which can be read from with tabledata.list.

Note: The client library avoids the extra call to `get_table` if query
results are read directly from the QueryJob, but it's confusing to show
that we're able to get the schema from a private API call to
getQueryResults.
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tswast authored Dec 12, 2019
1 parent 8f67bf8 commit 68c2cc8
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53 changes: 53 additions & 0 deletions bigquery/samples/query_pagination.py
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# Copyright 2019 Google LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.


def query_pagination(client):

# [START bigquery_query_pagination]
# TODO(developer): Import the client library.
# from google.cloud import bigquery

# TODO(developer): Construct a BigQuery client object.
# client = bigquery.Client()

query = """
SELECT name, SUM(number) as total_people
FROM `bigquery-public-data.usa_names.usa_1910_2013`
GROUP BY name
ORDER BY total_people DESC
"""
query_job = client.query(query) # Make an API request.
query_job.result() # Wait for the query to complete.

# Get the destination table for the query results.
#
# All queries write to a destination table. If a destination table is not
# specified, the BigQuery populates it with a reference to a temporary
# anonymous table after the query completes.
destination = query_job.destination

# Get the schema (and other properties) for the destination table.
#
# A schema is useful for converting from BigQuery types to Python types.
destination = client.get_table(destination)

# Download rows.
#
# The client library automatically handles pagination.
print("The query data:")
rows = client.list_rows(destination, max_results=20)
for row in rows:
print("name={}, count={}".format(row["name"], row["total_people"]))
# [END bigquery_query_pagination]
23 changes: 23 additions & 0 deletions bigquery/samples/tests/test_query_pagination.py
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# Copyright 2019 Google LLC
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# https://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

from .. import query_pagination


def test_query_pagination(capsys, client):

query_pagination.query_pagination(client)
out, _ = capsys.readouterr()
assert "The query data:" in out
assert "name=James, count=4942431" in out

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